Wave energy (i.e. the energy of periodically oscillating waves on an ocean, sea, lake or other large body of water) can be converted to electrical energy by using the waves' buoyant force to cause a floating body to oscillate (i.e. bob up and down with the waves). The buoyant force which the waves exert on the floating body must react against an opposing body to facilitate conversion of the floating body's kinetic energy into commercially useful energy. The seabed, or a piling embedded in the seabed and capable of withstanding wave loads, may serve as the opposing body. Such “single body” systems have only one floating body, and a stationary opposing body. The kinetic energy produced as the floating body oscillates relative to the stationary opposing body is converted to electrical energy by a generator coupled between the two bodies.
Single body systems are typically employed near shore, in relatively shallow water in which suitable piling or mooring structures can be provided to serve as a stationary opposing body for a floating body to react against. Single body systems are not well suited to deep water use, since it is difficult to provide deep water piling or mooring structures capable of withstanding the full range of hydrodynamic forces encountered in deep water wave environments. Near shore, the piling or mooring structure of a single body wave energy converter can also interfere with seabed ecosystems, which is undesirable.
“Two-body” wave energy converters typically provide a second floating body (or a submerged or semi-submerged body) to act in opposition to the first, or primary, floating body. A two-body wave energy converter can be slack-moored to the seabed, and is sometimes called “reactionless” since the slack mooring does not transmit to the seabed the reaction forces caused by oscillation of the primary and secondary bodies relative to one another.
Two-body wave energy converters are commonly designed to emulate the performance of single body systems, such that the second floating body remains relatively stationary and the generator is driven primarily by a single oscillating motion—that of the primary floating body. However it is advantageous to allow the primary and secondary bodies to oscillate longitudinally relative to one another, and to dynamically control such oscillation in response to changes of the wave environment in which the wave energy converter is deployed. As explained below, such control facilitates maximization of the relative motion between the primary and secondary bodies, increasing the driving force imparted to the generator and thereby increasing the generator's electrical energy output.